1. Field of the Invention
The present invention relates to a liquid droplet jetting apparatus such as an ink-jet printer.
2. Description of the Related Art
A tube-supply-type ink jet printer in which ink supplied from a detachable ink tank via a flexible ink supply tube is temporarily stored in a sub tank on a carriage, and the ink is supplied from the sub tank to a jetting head, and printing is carried out on a recording paper by jetting the ink from nozzles of the jetting head has hitherto been known (refer to U.S. Pat. No. 7,413,295 which corresponds to Japanese Patent Application Laid-open No. 2005-271546).
In this ink-jet printer, since the ink in the ink supply tube is accelerated by an inertial force by an acceleration and a deceleration of a carriage which reciprocates, a pressure wave from the ink in the ink supply tube is propagated to the ink in the jetting head. Moreover, when the ink is jetted from the jetting head, since an inside of the sub tank is depressurized due to a decrease in an amount of ink, a refill pressure, which acts so that the sub tank is refilled with the ink from the ink tank via the ink supply tube, is generated. When the ink is jetted simultaneously from a large number of nozzles, the pressure wave propagated to the nozzles of the jetting head due to the refill pressure becomes great. Further, when the pressure wave propagated to the nozzles becomes great, there is an adverse effect on a meniscus which is formed in each of the nozzles of the jetting head, and a printing quality is deteriorated. Therefore, an ink storage chamber of the sub tank is sealed by a damper film and a pressure fluctuation on the ink is absorbed.
However, when a printing speed is increased for improving a performance of the printer, a scanning speed of the carriage increases, and an ink flow increases. Therefore, in order to absorb the pressure fluctuation of the ink sufficiently, an area of the damper film has to be increased. However, since printers in recent years tend to be made smaller, increasing the area of the damper film is not practical. To deal with this problem, a structure, in which a drive-transmission rod is connected to a central portion of a surface of the damper film and a driving force is applied to the drive-transmission rod from an actuator according to a speed change of the carriage, has been proposed (refer to Japanese Patent Application Laid-open No. 2001-121713). According to this structure, by active deformation of the damper film, it is possible to absorb more effectively the pressure fluctuation, of the ink in the ink supply tube, which is generated when the carriage reciprocates.
However, according to the structure disclosed in Japanese Patent Application Laid-open No. 2001-121713, only for suppressing the pressure fluctuation of the ink in the sub tank, an actuator etc. has to be mounted on the carriage, which becomes rather expensive from a point of cost efficiency.